fix: allow empty statement bodies

Author: JoshuaKGoldberg

src/index.ts

@@ -4,7 +4,7 @@ import typescript from "prettier/parser-typescript";
 
 import { preprocess } from "./preprocess.js";
 
-export const parsers: Record<string, Parser> = {
+export const parsers = {
 	babel: {
 		...babel.parsers.babel,
 		preprocess,
@@ -13,4 +13,4 @@ export const parsers: Record<string, Parser> = {
 		...typescript.parsers.typescript,
 		preprocess,
 	},
-};
+} satisfies Record<string, Parser>;

src/modifyNodeIfMissingBrackets.ts

@@ -10,14 +10,17 @@ function wrapInBlock(node: Statement): BlockStatement {
 	};
 }
 
+const allowedBodyNodeTypes = new Set(["BlockStatement", "EmptyStatement"]);
+const allowedIfAlternateNodeTypes = new Set(["BlockStatement", "IfStatement"]);
+
 export function modifyNodeIfMissingBrackets(node: CollectibleNode) {
 	switch (node.type) {
 		case "DoWhileStatement":
 		case "ForStatement":
 		case "ForInStatement":
 		case "ForOfStatement":
 		case "WhileStatement":
-			if (node.body.type !== "BlockStatement") {
+			if (!allowedBodyNodeTypes.has(node.body.type)) {
 				node.body = wrapInBlock(node.body);
 				return true;
 			}
@@ -27,14 +30,14 @@ export function modifyNodeIfMissingBrackets(node: CollectibleNode) {
 		case "IfStatement": {
 			let modified: true | undefined;
 
-			if (node.consequent.type !== "BlockStatement") {
+			if (!allowedBodyNodeTypes.has(node.consequent.type)) {
 				node.consequent = wrapInBlock(node.consequent);
 				modified = true;
 			}
 
 			if (
 				node.alternate &&
-				!["BlockStatement", "IfStatement"].includes(node.alternate.type)
+				!allowedIfAlternateNodeTypes.has(node.alternate.type)
 			) {
 				node.alternate = wrapInBlock(node.alternate);
 				modified = true;

src/preprocess.test.ts

@@ -50,6 +50,7 @@ do{//a
 b}while(c);
 `,
 		],
+		[`for (; ; ) ;`, `for (; ; ) ;`],
 		[`for (; ; ) d;`, `for(;;){d}`],
 		[`for (; ; ) { d; }`, `for (; ; ) { d; }`],
 		[`for (a; b; c) d;`, `for(a;b;c){d}`],
@@ -95,6 +96,7 @@ c}`,
 		[`await 1;`, `await 1;`],
 		[`super;`, `super;`],
 		[`export { foo };`, `export { foo };`],
+		[`while (a) ;`, `while (a) ;`],
 		[`while (a) b;`, `while(a){b}`],
 		[`while (a) { b; }`, `while (a) { b; }`],
 		[`while (a) <b>c;`, `while(a){(<b>c)}`],